1. Field of the Invention
The present invention relates to impellers and fuel pumps that are provided with an impeller.
2. Description of the Related Art
Japanese Laid-open Patent Publication No. 2003-193992 discloses an impeller. The impeller is formed in a disc shape and includes an upper face and a lower face. Concavities are repeatedly arranged along a circumference direction on the upper face and the lower face. The impeller rotates centered on an axis of rotation. FIG. 15 is an enlarged drawing of the concavities 100 of a conventional impeller, and shows a plan view in which the concavities are viewed from the opening side. The arrow 105 in FIG. 15 indicates the direction of rotation for the impeller. In the present specification, a direction of rotation of the impeller is denoted by the term “front”, and the direction opposite thereto is denoted by the term “back”. In FIG. 15, the direction of the arrow 105 is oriented toward the “front”, and the direction of the arrow 106 is oriented toward the “back”. The arrow 107 in FIG. 15 is oriented in the direction toward the center of rotation of the impeller, and the arrow 108 in FIG. 15 is oriented in the direction toward the exterior of the impeller. In the present specification, the direction toward the center of rotation of the impeller (i.e., the direction of the arrow 107) is denoted by “inner”, and the direction toward the exterior of the impeller (i.e., the direction of the arrow 108) is denoted by “outer”. Therefore, among the sections of the inside surface of each concavity 100, reference numeral 101 denotes a “front surface”, reference numeral 102 denotes a “back surface”, reference numeral 103 denotes an “inner surface”, and reference numeral 104 denotes an “outer surface”. The back surface 102 of the concavity has a concave shape. The front surface 101 of the concavity has a convex shape. In addition, the concavity has a bottom surface.
Normally, this impeller is installed so as to be rotatable within a pump casing. On the inside surface of the pump casing, a groove is formed that extends from an upstream end to a downstream end of an area that is opposite to the group of concavities of the impeller. When the impeller is installed in the pump casing, a fuel path is formed by the group of concavities of the impeller and the groove that is formed on the inside surface of the pump casing. When the impeller rotates inside the pump casing, fuel is drawn into the fuel path. The fuel that has been drawn into the fuel path is subject to a centrifugal force caused by the rotation of the impeller. Thereby, the fuel swirls between the concavities of the impeller and the groove of the pump casing (that is, within the fuel path), and flows through the groove of the pump casing from the upstream side to the downstream side. Thereby, the fuel pressure increases, and this pressurized fuel is discharged from the downstream end of the fuel path to the outside of the pump casing.